To interact with the enzyme, the substrate must be able to fit into the active site.

• There must be suitable charges on the substrate if there are any charged R-groups on amino acids inside the active region of the enzyme.

• An active site containing positively charged amino acids, for example, would resist any positively charged molecules, even if the molecule's form could fit in the active site of the enzyme.

• Enzymes catalyze reactions more efficiently at specified enzyme-specific temperatures and pHs.

If the temperature in the environment is too low, the rate of collisions between the enzyme and its substrate slows, and the process slows.

• When the temperature is too high, the bonds that keep the enzyme together are broken.

• Similarly, a pH that is too high might break enzyme linkages, resulting in a change in the enzyme's tertiary structure.

  Changes in an enzyme's ionic environment can potentially break bonds in the enzyme.

• Denaturation is a change in the structure of an enzyme that can restrict the enzyme's capacity to catalyze chemical processes.

• Denaturation can sometimes, but not always, be reversed when the environment returns to more ideal circumstances.

Competitive inhibitors resemble substrates in form and compete with substrates for an enzyme's active site.

• Noncompetitive (or allosteric) inhibitors bind to a different place on the enzyme than the active site (called the allosteric site).

• The noncompetitive inhibitor's binding.

• The noncompetitive inhibitor's binding to the allosteric site modifies the structure of the enzyme, changing its activity.

• Because the noncompetitive inhibitor does not bind to the active site of the enzyme, increasing the concentration of substrate has no effect on the inhibitor's function.

• Noncompetitive inhibitors can work as feedback mechanisms, modifying the pace of chemical processes in the cell in response to changing environmental variables.

Life needs a steady supply of energy to run cellular operations and keep living systems in order.

• To maintain life, the energy intake into the cell must be larger than the energy requirements of the cell.

• Energy-releasing activities can be linked (or coupled) with energy-requiring ones.

These linked reactions take place in a series of stages to allow for the regulated transfer of energy between molecules, resulting in greater efficiency.

• While enzymes can reduce reaction activation energy, they cannot convert an endergonic reaction to an exergonic reaction.

• Enzymes are incapable of converting an energetically unfavorable reaction into an energetically favorable one.

• To initiate a chemical reaction, energy input is required to achieve a transition state.

The activation energy (EA) is the difference in energy levels between the reactants and the reaction's transition state.

• Higher activation energies cause slower chemical reactions; lower activation energies allow for quicker chemical reactions.

• Enzymes accelerate chemical processes by decreasing the reaction's activation energy.

• Exergonic reactions produce products with lower free energy levels than their reactants and are thus regarded energetically advantageous.